Building noise control - flanking pathways:

This article explains how sound flanking paths, sound leaks around and through building components, defeats incomplete attempts to reduce building sound transmission and noise levels. We include design details for sound reducing details in buildings including soundproof office doorways and doors.

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) , by Steven Bliss, courtesy of Wiley & Sons.

How to Cut Off Flanking Paths for Sound

Definition of flanking transmission or flanking sound transmission

Definition of flanking transmission or flanking noise transmission: the term flanking transmission in acoustical engineering is used to describe the passage of sound over, under, or around barriers intended to provide sound or noise control or isolation.

[Click to enlarge any image]

For example if sound-transmission-resistant partitions have been constructed between rooms but there are openings at the partition wall top (perhaps through a suspended ceiling) then sound control may be ineffective as sounds can pass over the intended noise barrier.

The page top photograph shows a pair of solid core doors installed at the entry to an office where sound transmission and privacy are a concern. Below we provide more details about soundproofing at doorways.

Continuing from from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) :

Sound takes the path of least resistance between rooms, through any air leaks or through rigid connections in the structure itself. These routes that bypass efforts at sound insulation are called flanking paths.

These flanking transmission pathways can significantly reduce the effectiveness of soundproofing efforts.

Building walls with high STC ratings (SOUND TRANSMISSION CLASS RATINGS) will do little good if sound can pass easily though electrical outlets or a thin, loosely fitting door.

For example, an un gasketed door or the equivalent of a one-inch-square hole in a wall can reduce an STC 50 wall to STC 30.

Checklist of Common Flanking Transmission Pathways in Buildings

Our photo shows a sneaky flanking noise path - an under-cut door to a room used for massage treatment. Even though the door is solid wood, gaps around the door and the especially wide gap below the door provide a flanking noise pathway.

Common flanking paths include:

• Bathroom medicine cabinets - back-to-back medicine cabinets,
• Ceilings: Air leakage around partition walls at ceilings;
• Doors: Air and thus sound leaks around doors. Hollow-core doors and single-pane glass, are good sound transmitters.
• Ductwork: shared ductwork between two rooms
• Electrical receptacles & light switches: unsealed electrical outlets
• Floor noise transmission; for example even with sound isolation between floor levels in a building, if solid floor coverings such as subfloor or finish wood planking extend beneath partitions and into an adjoining area that forms a sound flanking pathway
• Framing connections that include solid framing members passing between building areas are noise transmission conduits; Even in a de-coupled framing design intended to address flanking noises, de-Coupled framing omissions: with decoupled framing, a solid path through a band joist or drywall panel provides a bypass for structure-borne sound.
• Partition edge abutments to adjoining walls, ceilings, floors
• Plumbing penetrations: Air leaks & sound flanking through plumbing penetrations. Also plumbing chaseways that pass between building areas horizontally or vertically
• Recessed light fixtures
• Resilient channel connector mistakes: with resilient channels, a few drywall screws that penetrate into the ceiling joists, undermining the decoupling system.
• Window noise transmission

How to minimize Flanking Transmission of Noises

Minimizing sound noise transmission flanking paths requires both good planning and workmanship. Common strategies to control flanking path for noise in buildings include:

• Avoid back-to-back holes for electrical and mechanical equipment.
• Partition wall sealants: Along partition bottoms, leave a 1/4-inch gap between the drywall and subfloor, and fill with acoustical sealant.
• Bathroom noises:
• On bathroom partitions, install drywall all the way to the floor before installing the tub and seal all plumbing penetrations through walls with a flexible sealant
• Bathroom doors: avoid hollow-core doors (photo at left), use solid wood or sound-resistant doors
• For warm air heat or air conditioned bathroom spaces provide return air by ducting; undercutting a door (photo at left) to permit return air flow out of the bathroom provides a flanking sound pathway.

Design Details for Soundproof Doors & Doorways

This topic has been moved to SOUND CONTROL for DOORS.

- - Adapted with permission from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) .

...

Continue reading at SOUND CONTROL for AIR DUCTS, HVAC or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• HEATING SYSTEM NOISE DIAGNOSIS
• NOISE / SOUND DIAGNOSIS & CURE - home
• SOUND CONTROL in BUILDINGS - home
  • ACOUSTICAL SEALANT CHOICES
  • COMPRESSOR MOTOR INSULATION
  • FLANKING SOUND PATHWAY CUT-OFF
  • ROOF NOISE TRANSMISSION
  • SOUND ABSORPTION vs. SOUND ISOLATION
  • SOUND CONTROL for AIR DUCTS, HVAC
  • SOUND CONTROL for DOORS
  • SOUND CONTROL for FLOORS
  • SOUND CONTROL for PLUMBING
  • SOUND CONTROL for WALLS
  • SOUND EVENT LOG
  • SOUND LEVEL MEASUREMENT, HOW TO
  • SOUND & NOISE TRANSMISSION PRINCIPLES
  • SOUND TRANSMISSION CLASS RATINGS
  • SOUNDPROOFING MATERIAL PROPERTIES
  • WHITE NOISE & SOUND CONDITIONERS
• SOUND EVENT LOG

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FLANKING SOUND PATHWAY CUT-OFF at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING NOISE DIAGNOSIS

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